a. Technical Field
The instant disclosure relates generally to power electronics systems, and more particularly to an isolated AC/DC electric power conversion apparatus.
b. Background
This background description is set forth below for the purpose of providing context only. Therefore, any aspects of this background description, to the extent that it does not otherwise qualify as prior art, is neither expressly nor impliedly admitted as prior art against the instant disclosure.
Isolated alternating current (AC)/direct current (DC) electric power converters can be used in many different applications. For example only, such an electric power converter can be used as a battery charger to charge a DC battery associated with an electric-motor powered automotive vehicle. Known isolated AC/DC electric power converters may adopt three main stages. For example, FIG. 14 shows a typical configuration, namely, a half-bridge resonance based isolated AC/DC converter 1400. The converter 1400 may include a first stage 1410, a second stage 1420, and third stage 1430.
The first stage 1410 may be an AC/DC converter stage configured to convert grid or mains AC voltage (e.g., 50 or 60 Hz), which is shown as being provided by an AC source 1440 through an input inductor 1442, to an output DC voltage at node 1444. The first stage 1410 may use a rectifier 1446 whose switches can be controlled to implement power factor correction (PFC). The DC voltage at node 1444 is stored across a relatively large storage capacitor 1448.
The second stage 1420 may perform a DC/AC converter function that is configured to transform the rectified DC voltage to a relatively high-frequency AC voltage (e.g., hundreds of kHz). The high-frequency AC voltage in turn is applied to an electrical isolation device—shown as a transformer 1450, which has a primary winding 1452 and a secondary winding 1454. An inductor 1456 and capacitors 1458, 1460 form a resonance circuit to realize zero voltage switching (ZVS).
The third stage 1430 may perform a further AC/DC converter function, and which may include a rectifier 1462 (e.g., four diode, full wave bridge shown) configured to rectify the high-frequency AC voltage signal induced on the secondary side 1454 of the transformer 1450. The rectifier 1462 thus produces a final DC output voltage signal on node 1464. The target battery in this example is arranged to receive the final DC output voltage signal, which is shown as including a DC voltage source part 1466 and an internal battery resistance 1468.
Since the three main stages of the above-described converter 1400 are electrically connected in series, the system efficiency will ultimately be reduced. For example only, assume that stage 1410 (i.e., the PFC part) and stage 1420 (i.e., DC/AC converter part) each have a 98% efficiency, and that stage 1430 (i.e., the battery-side AC/DC converter part) and the transformer 1450 each have a 99% efficiency. Given these assumption, an overall system efficiency may be approximately 98%*98%*99%*99%=94.1%. In addition, the 3-stage converter described above incorporates a relatively large, bulky DC capacitor 1448, which can diminish power density and which can reduce a service life of the overall AC/DC electric power converter.
It would be desirable to improve the overall system efficiency, as well as increase power density and extend service life.
The foregoing discussion is intended only to illustrate the present field and should not be taken as a disavowal of claim scope.